Sieve plate for manufacture of fiber board and similar board products



'Oct. 11, 1966 K. e. MALM ETAL 3,277,814

SIEVE PLATE FOR MANUFACTURE OF FIBER BQARD AND SIMILAR BOARD PRODUCTS Filed oct. o, 1964 KARL GUNNAR MALM and ROLF BERTIL REINHALL Inventor-s 5y Ema Y. MUNSON United States Patent 3,277,814 STEVE PLATE FOR MANUFACTURE OF FIBER BOARD AND SIMILAR BOARD PRODUQTS Karl Gunnar Malm, Grastorp, and Rolf Bertil Reinhall, Lidingo, Sweden, assignors to Defibrator Aktiebolag, Stockholm, Sweden, and Aktiebolaget Knntsilsplatar, Grastorp, Sweden, both corporations of Sweden Filed Oct. 20, 1964, Ser. No. 405,131 Claims priority, application Sweden, Oct. 21, 1963, 11,547/63 1 Claim. (Cl. 100-295) This invention relates to sieve plates for manufacture of board.

More particularly this invention relates to sieve plates for manufacture of primarily hardboard, but also other board products such as fiber board, particle board and similar products.

The manufacture of these types of board is conducted so that on the sieve plates there are placed wet sheets, i.e. sheets or layers of the water containing fiber pulp of which the 'boards are to be made. The sieve plates with their wet sheets are then introduced between press platens in a press to which heat is supplied, the water being removed partly through squeezing and partly through evaporation.

It is known to use for this purpose sieve plates which are provided with elongated slots disposed in mutually parallel rows through which the water and/ or the steam are drained off. The slots may in turn on the rear side of the sieve plate communicate with substantially transversal grooves extending to the border edge of the sieve plate. The removal of the water and the steam during the press operation may instead be effected by means of a wire screen or the like means disposed below the sieve plate.

When the sieve plates with the wet sheets resting there on begin to be exposed to the treatment in the press, a rise of temperature is caused in the plates. At the same time the plates are exposed to a powerful pressure action. Both actions result in that the plate is locked in its position while it at the same time tends to expand due to the rise of its temperature. Thereby stresses are created in the plate which often result in that the plate is weakened, in some cases so much that fractures or fissures are formed adjacent the slots.

One main object of the invention is to eliminate said drawback inherent in sieve plates of the type under consideration. According to one main feature of the invention the slots in one row are disposed to overlap the slots in an adjacent row so that the sieve plate in every section transverse to the longitudinal direction of the slots is interrupted by a plurality of slots. In this way the sieve plate is divided up into zones possessing a local capacity of movement in the plane of the plate. A thermal extension can thus occur in each zone without necessarily being propagated through the entire plate for which reason concentrations of tension cannot be produced at any place of the plate surface.

The sieve plates are usually rectangular and therefore it is particularly suitable to provide the slots extending perpendicularly to one longitudinal edge of the plate.

Further objects and advantages of the invention will become apparent from the following descriptions considered in connection with the accompanying drawing which forms part of this specification and of which:

FIG. 1 is a partial top view of a sieve plate embodying the invention and FIG. 2 is a sectional view following line II-II of FIG. 1.

Referring to the drawing, a sieve plate 4 is provided with elongated slots 5 which are mutually parallel and arranged in rows displaced relatively to one another in such a manner that the unbroken plate portions S between the slots 5 in one row are overlapped by the slots 5 of adjacent rows. The length of the slots 5 is at least twice and most suitably three times as great as the longitudinal dimension of the plate portions S i.e. the spacing between two slots in the same row. This results in that the sieve plate in each section AA taken over the whole plate surface is many times interrupted by slots whereever this section may be assumed to be located.

When the sieve plate upon having been positioned with its wet sheet placed thereon between the press platens of a multi-store press for example and been exposed to pressure and heat, local movements of plate material within the plate will occur, but these are limited to the overlapping portions of four adjacent slots 5 and 5 The plate surface will thus be divided up into a very great number of smaller zones which each takes care of the thermal expansion within its region. The movements of the various zones will result in that the slots are reduced in their width. Of course this reduction is, calculated in measure units, very small but has as its consequence that all such concentrations of tension in the plate material which could cause fractures or fissures, are effectively avoided. If the sieve plates are of oblong shape which mostly is the case, their longitudinal direction should preferably coincide with the section line A-A so that the slots mainly are operative in that direction where most of the thermal expansion is acting.

The slots 5 may on the rear side of the sieve plate be in communication with grooves 6 extending transversely to the longitudinal direction of the slots. These grooves facilitate the drainage of the water escaping in the state of liquid or steam through the slots 5. If desired, the slots may have a portion 7 of constant width directly adjacent the operative side of the plates, said portion thereupon merging into a portion 8 of a width increasing towards the rear side.

While one more or less specific embodiment of the invention has been shown and described, it is to be understood that this is for purpose of illustration only, and that the invention is not to be limited thereby, but its scope is to be determined by the appended claim.

What we claim is:

A sieve plate for the manufacture of fiber board and similar board products by pressing of wet sheets positioned on the plate between heated press platens in a press, said sieve plate having front and rear faces and being formed with spaced rows of spaced slots, the slots in one row being parallel to those in adjacent rows, the slots in one row being located with their ends overlapping the slots in an adjacent row, the walls of each slot diverging from the front face of the plate toward the rear face thereof so that each slot is larger at its rear end than at its front end, the plate having open drainage grooves formed directly in it in its rear face, said grooves extending transversely of the slots and each groove transversely crossing the slots in one row only and located between the ends of the slots in two adjacent rows, each of the grooves being open at the bottom at the surface of the rear face of the plate.

References Cited by the Examiner UNITED STATES PATENTS 1,247,941 11/1917 Douthat et al -115 X 1,540,325 6/ 1925 Fuller. 1,553,310 9/1925 Ellis 100115 X 1,631,585 6/1927 DOlier et a1. 210498 2,854,896 10/1958 Marton 100-115 X 2,866,556 12/1958 Hinz 210-498 FOREIGN PATENTS 48,541 10/ 1930 Norway.

LOUIS O. MAASSEL, Primary Examiner. 

